4.2.1.4. Diapause
As Artemia is an inhabitant of biotopes characterized by unstable environmental conditions,
its survival during periods of extreme conditions (i.e. desiccation, extreme temperatures, high
salinities) is ensured by the production of dormant embryos. Artemia females can indeed
easily switch from live nauplii production (ovoviviparity) to cyst formation (oviparity) as a fast
response to fluctuating circumstances. Although the basic mechanisms involved in this
switch are not yet fully understood, sudden fluctuations seem to trigger oviparity (oxygen
stress, salinity changes...). The triggering mechanism for the induction of the state of
diapause is however not yet known. In principle, Artemia embryos released as cysts in the
medium are in diapause and will not resume their development, even under favourable
conditions, until they undergo some diapause deactivating environmental process; at this
stage, the metabolic standstill is regulated by internal mechanisms and it can not be
distinguished from a non-living embryo. Upon the interruption of diapause, cysts enter the
stage of quiescence, meaning that metabolic activity can be resumed at the moment they are
brought in favourable hatching conditions, eventually resulting in hatching: in this phase the
metabolic arrest is uniquely dependent of external factors (Fig. 4.2.4.). As a result,
synchronous hatching occurs, resulting in a fast start and consequent development of the
population shortly after the re-establishment of favourable environmental conditions. This
allows effective colonization in temporal biotopes.